360 



EMBRYOLOGY 



side by a broad space. The ventral and dorsal parts of the 

 trunk-plate now grow out more and more on the sides, and 



Fig. 158. — .1 to F, stages of development of Sipunculus nudus (after Hatschek). 

 -•1, blastula ; B, gastrula ; C to E, other stages, in which the development of the head- 

 and trunk-plates takes place ; F, embryo during hatching ; a, anus ; bl, blasto- 

 pore ; (Ir, glandular appendage of the fore-gut; cct, ectoderm; ent, entoderm ; lia, 

 liead amniotic cavity; m, month; mcs, mesoderm; n, nephridium; ra, trunk 

 amniotic cavity ; rp, trunk-plate; s, pharynx; se, serosa; so, somatic, sp, splanch- 

 nic, layer of the mesoderm ; w, ciliated band. The ectoderm is finely and the ento- 

 derm cjarsely punctate ; the mesoderm is cross-hatched. 



